Hydrophobizing agents are widely used to impart water resistance to such compositions as textiles, carpet fibers, paper and paperboard, when applied thereon. Many materials are known in the art to be useful as hydrophobizing agents for water repellency applications, including organometallic complexes, waxes and wax-metal emulsions, resin-based finishes, silicones, rosin, alkylketene dimers, and fluoro chemicals. A general review of the many uses and types of water repellent chemicals, useful as hydrophobizing agents, is provided by M. Hayek in the Encyclopedia of Chemical Technology, Volume 24, (1984), "Waterproofing and Water/Oil Repellency", pages 442 through 465, and is incorporated herein by reference.
It is well known in the art that many hydrophobizing agents can be stabilized in aqueous dispersion form by the presence of surfactants, usually fatty acid salts, or salts of sulfated fatty alcohols, in order to facilitate their handling and application onto materials, especially at surfaces or at interfaces, for the purpose of imparting water repellency. Such dispersions contain relatively high concentrations of surfactant and/or protective colloids as dispersion stabilizers, typically greater than 10% by weight based on hydrophobizing agent, the presence of which, while providing the necessary colloidal stability for practical preparation of such aqueous dispersions, and providing the necessary surface activity to ensure deposition of the hydrophobizing agent at surfaces or interfaces, can detract from the repellency properties desired upon final application. This results from the presence of the usually hygroscopic surfactant or protective colloid in the resulting water repellent layer, which can promote rewetting and swelling of the deposited hydrophobizing agent in the presence of water or water vapor.
In the case of reactive hydrophobizing agents, such as fatty acid anhydrides, alkylketene dimers, and alkenylsuccinic anhydrides, or blends of reactive hydrophobizing agents with themselves or with nonreactive hydrophobizing agents, wherein covalent bonds with active hydrogen-containing groups on the surface of substrates can be formed to provide an enhanced hydrophobizing effect, the high levels of dispersion stabilizers required for colloidal stability can interfere with the covalent reactions anchoring the repellent to the substrate by competing with the substrate for active sites, lessening the hydrophobizing effect. Reaction of the reactive hydrophobizing agent with water itself also poses significant problems in designing stable dispersions of such materials. In addition, the high levels of emulsifiers can serve to increase the rate of the hydrolysis side reaction, resulting in dispersions of limited shelf life.
In the case of crystalline reactive hydrophobizing agents or blends of crystalline reactive hydrophobizing agents with themselves or with crystalline or amorphous hydrophobizing agents such as the various natural, mineral, and synthetic waxes, and fatty triglycerides, substantially higher levels of dispersion stabilizer are frequently required to offset the pronounced negative effect the presence of the crystalline hydrophobizing agent has on dispersion stability. Indeed, it is known that incorporation of even low levels of crystalline hydrophobizing agents into aqueous dispersions frequently causes a dispersion of amorphous hydrophobizing agent to gel upon standing. Thus shipping, storage, and handling requirements require that high levels of dispersion stabilizer be used to ensure sufficient colloidal stability to prevent dispersion flocculation, viscosity build, and eventual gelation or solidification. Nevertheless, crystalline hydrophobizing agents, and crystalline reactive hydrophobizing agents in particular, provide a high degree of water repellency and it is frequently a goal of manufacturers of hydrophobizing agent dispersions to blend crystalline hydrophobizing agents or crystalline reactive hydrophobizing agents with less costly crystalline or amorphous hydrophobizing agents to achieve a proper balance of economics and high performance. It is therefore desirable to minimize the presence of dispersion stabilizing additives, such as surfactants or protective colloids, in the final reactive hydrophobizing agent dispersion, in order to achieve the greatest efficiency of active ingredient utilization.
One method for providing such colloidal stability, in addition to the aforementioned use of high levels of surfactants, has been to prepare the dispersions in relatively dilute form, usually less than 10% to 20%, by weight based on total dispersion, of reactive hydrophobizing agent or reactive hydrophobizing agent blend. While this may provide sufficient stability for many applications, it can also lead to inefficiencies in storage and shipping since the corresponding quantity of water becomes excessively large, requiring surplus storage facilities and shipping containers for what amounts to low levels of useful or active ingredient. It is therefore also desirable to maximize the concentration of reactive hydrophobizing agent or reactive hydrophobizing agent blend in the dispersion, to provide the greatest efficiency of storage and to minimize transportation costs.
Numerous patents have been obtained disclosing methods for improving the colloidal stability, i.e. storage and handling stability, of dispersions containing reactive hydrophobizing agents. Thus U.S. Pat. No. 4,296,012 describes a method of utilizing a non-crystalline hydrocarbon resin in combination with a crystalline ketene dimer in order to achieve the appropriate amount of stability in the corresponding aqueous ketene dimer dispersion, while providing a high degree of sizing effect. However, the dispersions are relatively dilute, typically 15% by weight of total dispersion of non-volatile component and contain a high concentration of dispersion stabilizer, typically greater than 20% by weight based on concentration of hydrophobizing agent.
A combination of a cationic dispersing agent and alkyl hydroxyalkyl cellulose, as dispersion stabilizers for substituted ketene dimer dispersions, is disclosed in U.S. Pat. No. 3,931,069. The dispersions are useful for sizing cellulose fibers and contain up to 30%, by weight, of total solids content, of which the ketene dimer content is substantially less than 30% by weight.
Furthermore, it had been disclosed and claimed in U.S. Pat. No. 2,627,477 aqueous emulsions of higher ketene dimers, containing a water-soluble cellulose ether, useful in sizing paper. However the examples teach that very high levels of water-soluble cellulose ether relative to ketene dimer, up to as much as 300% or greater by weight of stabilizer based on ketene dimer, must be employed. The resulting dispersions themselves are very dilute, typically 0.5% by weight of ketene dimer based on total dispersion.
U.S. Pat. No. 5,013,775 discloses the difficulty associated with preparation of stable high concentration aqueous dispersion sizing agents based on ketene dimer compounds and suggests a solution whereby a composition comprising a hydrophilic copolymer polymerized in the presence of an alkylmercaptan is utilized to stabilize the hydrophobic ketene dimer compounds in aqueous dispersion form. The resulting dispersions typically contain about 20% solids by weight of total dispersion and 20% dispersion stabilizer by weight of ketene dimer.
U.S. Pat. No. 5,028,236 describes ketene dimer dispersions useful for the treatment of wool and synthetic polyamide fibers. The dispersions of said invention are less than about 10%, by weight of total dispersion, of hydrophobizing agent.
U.S. Pat. No. 5,403,392 describes high solids dispersions of hydrophobizing agents stabilized in aqueous dispersion form by plant glycosides. The dispersions of said patent are stable upon storage at ambient conditions and achieve hydrophobizing agent concentrations of up to about 40% by weight of total dispersion.
U.S. Pat. No. 5,658,377 describes high solids dispersions of hydrophobizing agents produced utilizing water-soluble protective colloids in combination with hydrolytically stable water-insoluble organic compounds selected from the group comprising organic salts and polar group-containing organic compounds. The dispersions of said patent are stable upon storage at ambient conditions and achieve hydrophobizing agent concentrations of up to about 50% by weight of total dispersion.
From the related field of nonreactive wax emulsions, several other U.S. patents describe methods of producing high solids wax dispersions. For instance, U.S. Pat. No. 2,172,392 discloses stable high solids wax emulsions produced in the presence of high levels of protein materials such as casein. Salts such as sodium carbonate are used to solubilize the protein materials in water via ionization of their carboxyl groups, enabling the protein's emulsifying properties to be manifested. Very high levels of emulsifier are used to achieve the desired effect.
U.S. Pat. No. 2,536,018 relates to aqueous polyvinyl acetate coating compositions modified by blending with wax emulsions to achieve improvements in wear resistance to objects coated therewith. Wax emulsions stabilized with fatty acid soaps are described.
U.S. Pat. No. 2,658,004 describes blends of wax emulsions and mica dispersions useful as last slips. No special requirements concerning the manufacture of the wax emulsion component nor of the mica dispersion component of the resulting blend are disclosed.
U.S. Pat. No. 3,432,319 discloses paraffin wax emulsion compositions comprising relatively low concentrations of a hydroxyalkyl methylcellulose ether dispersion stabilizer. Several advantages associated with the absence of conventional surfactants and the use of high aqueous concentrations of wax are disclosed, including increased mechanical shear stability and increased compatibility with urea-formaldehyde resins. However the hydrophobizing wax material is restricted to paraffin wax.
Finally, a detailed description of the complex considerations necessary in the design of stable industrial emulsions, including wax emulsions, is provided by W. C. Griffin in the Encyclopedia of Chemical Technology, Volume 8, (1979), "Emulsions", pages 900 through 930. This reference discloses that wax emulsions, i.e. dispersions, may be stabilized against agglomeration by buffering with an organic ester, although no details are given.
None of the aforementioned references describe the unique ability to simultaneously achieve aqueous emulsions which possess high reactive hydrophobizing agent or reactive hydrophobizing agent blend concentrations, low emulsifier content, high emulsion stability, and which impart enhanced water repellency characteristics to substrates according to the instant invention.